Apparatus for displaying the energy distribution of a charged particle beam

ABSTRACT

An energy display apparatus for plasma loss and plasma shift measurements. The electron beam transmitted through a thin foil alloy specimen at various irradiating points of a uniform energy electron beam is analyzed and the distribution is displayed on the screen of a cathode-ray tube. The base line of the energy distribution curve on the screen of a cathode-ray tube is shifted according to the location of the irradiating point.

United States Patent Kokubo 1 Sept. 30, 1975 [5 APPARATUS FOR DISPLAYING THE 3,626.l84 12/1971 Crewe .4 250/305 3,8l2,288 5/1974 Walsh 250/311 ENERGY DISTRIBUTION OF A CHARGED PARTICLE BEAM Yasushi Kokubo, Akishima, Japan Nihon Denshi Kahushiki Kaisha, Akishima. Japan Filed. Aug. 8, 1974 Appl. No.: 495,665

Inventor:

Assignce:

Foreign Application Priority Data Aug. 22, [973 Japan 4894l70 U.S. Cl 250/305; 250/310 Int. Cl. v. HOL] 37/26 Field of Search 250/3 l0, 3l l, 306, 307,

References Cited UNITED STATES PATENTS 6/l965 Crewe 250/31 l Primary Examiner-Craig E. Church Attorney, Agent, or FirmWebb, Burden, Robinson & Webb 2 Claims, 5 Drawing Figures SAWTOOTN WAVE FBZH 10X JJOY AtmmG CHICUIT US. Patent Sept. 30,1975 Sheet 10m 3,909,610

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APPARATUS FOR DISPLAYING THE ENERGY DISTRIBUTION OF A CHARGED PARTICLE BEAM This invention relates to an improved apparatus for displaying the energy distribution of a charged particle beam.

Formerly, in the study of compound metals, a commonly adapted measuring means was to measure the energy loss (hereinafter referred to as the plasma loss) of the electron beam due to plasma oscillation at the crystal grain boundary. Since the plasma loss varies according to the constituent components and phase of the alloy in question, the plasma loss and plasma shift values can be measured and the characteristics of the alloy can be ascertained by analyzing the energy of an electron bcam transmitted through a thin foil alloy specimen at a plurality of irradiating points of the high speed, uniform energy electron beam, and comparing the energy distribution at each irradiating point positioned, for example, along a line intersecting the grain boundary. In the prior art, the energy distribution at the respective irradiating points was recorded on photographic plates and the density distribution was measured plate by plate by means of a micro-photometer (densitometer). However, this method is extremely time consuming as micro-photometry has to be carried out as many times as there are irradiating points; moreover, micro-photometric measurement does not enable one to ascertain exactly how far the energy distribution is located from the grain boundary. Another disadvantage is that it is difficult to carry out comparison of the entire distribution waveforms.

It is therefore an object of this invention to provide an energy display apparatus capable of displaying exactly how far the energy distribution is located from the grain boundary. Another object of this invention is to facilitate the comparison of the entire distribution waveforms.

BRIEF DESCRIPTION This invention relates to an improvement in an imag ing device comprising means for scanning a high energy beam over a specimen in a raster in the X and Y directions by X and Y axis deflecting devices, for example, a scanning electron microscope. A detector detects a signal indicative of the interaction of the high energy beam and the specimen and modulates the beam of a C.R.T., the deflection devices of which are in synchronism with the high energy beam scanning device. In this way, a specimen image is produced.

Associated with said specimen imaging device is an energy analyzer for detecting the distribution of energies of the high energy beam after interaction with the specimen. The specimen imaging apparatus is disabled and a step signal generator stepwise applies a signal to the X deflection device of the high energy beam to cause it to advance stepwise over the specimen. While the beam is applied to a given point on a specimen, the energy levels detected by the energy analyzer are swept by a sawtooth signal applied thereto by a sawtooth gen erator. In this way, the detector of the energy analyzer detects a signal indicative of a range of energies for each point on a specimen. The output of the step signal generator and the energy analyzer are added and applied to the Y axis of the deflection device of the C.R.T. The sawtooth output of the sawtooth generator which is synchronized with the step signal generator is applied to the X axis deflection device of the C.R.T. In

this way, energy distribution curves for spaced points on a specimen are displayed on the CRT. separated by a Y axis shift enabling ready analysis of energy curve changes as the specimen is stepwise traversed by the high energy beam.

These and other objects and advantages of this invention will become apparent by reading the following de tailed description in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic diagram showing one embodiment according to this invention;

FIGS. 2a and 2b are schematic drawings for explaining the function of the embodiment shown in FIG. 1;

FIG. 3 is a schematic diagram showing the electron beam irradiating positions near grain boundary of the specimen; and,

FIG. 4 is a schematic drawing showing energy distribution on the display screen of the embodiment shown in FIG. 1.

Referring to FIG. I, an electron beam 1 generated by an electron gun 2 is finely converged by condenser lenses 3 and 4 so as to irradiat e a specimen 5. Deflection coils 6X and 6Y are arranged between the condenser lenses 3 and 4, the magnetic field produced by said deflection coils serving to deflect the electron beam I and therefore vary the specimen irradiating position. Switches S, and S are arranged so as to connect the deflection coils 6X and 6Y to the X and Y signals ofa sawtooth waveform generator 7 or the DC. voltage ofa DC. voltage source 8 and the Y signal of a step signal generator 9. Further, a portion of the X and Y signals from the sawtooth waveform generator 7 are fed into the X-axis deflection coil 10X and the Y-axis deflection coil l0Y of a cathode-ray tube 11 via switches S3 and S4. A secondary or reflection electron detector 12 is arranged in the vicinity of the specimen 5 and the output of said detector is applied to the grid of the cathode-ray tube 11 via an amplifier l3 and a switch S An energy analyzer 14 for energy analyzing the electrons transmitted through the specimen 5 is arranged below said specimen beyond which a slit 1S and a second detector 16 are provided. A sweep signal generator 17 generates a sawtooth wave signal as shown in FIG. 2(a), said sawtooth wave signal being fed into the energy analyzer 14. By so doing, the electrons separated at each energy level in the analyzer pass through the slit IS sequentially and enter the detector 16. Part of the output of the sweep signal generator 17 is applied to the X-axis deflection coil 10X of the cathode-ray tube 11 via switch S Further, the output of the detector 16, after being amplified by the amplifier 18, is fed into an adding circuit 19 and added to the signal from the step signal generator 9. The added output of the adding circuit 19 is then applied to the Y-axis deflection coil IOY of the cathode-ray tube 11 via switch S... A step signal is generated by the step signal generator 9, as shown in FIG. 2(b), in synchronism with the signal generated by the sweep signal generator 17. When switch S is positioned at T so that said step signal is fed into deflection coil 6Y and the electron beam is shifted stepwise as indicated by points p p p p in FIG. 3. In FIG. 3, the wavy line 0-0 shows the grain boundary. the A and B represent the grain constituting the alloy, and line P shows the direction of the said points p Pg, 2 p, crossing the grain boundary OO'. Since switches S, 5,, are interlocked, when they are positioned at T the electron beam 1 scans the specimen 5 over a specific area of the specimen surface and the secondary electrons etc. are detected by the detector 12, converted into an electrical signal, amplified by amplifier l3 and applied to the grid of the cathode-ray tube 11 as brightness modulation signal. Accordingly, a scanning image of the specimen is displayed on the screen of the cathode-ray tube 11. The portion or portions of the image where it is desired to measure the plasma loss is/are then selected and adjusted (i.e., focused and centered) with the appropriate controls.

On the other hand, when switches S S S and S, are positioned at T the signal from the step signal generator 9 is fed into deflection coil 6Y, and the signal from the sweep signal generator I7 is fed into coil X of the cathode-ray tube II, and the signal from the adding circuit 19 is applied to coil IOY of said cathode-ray tube ll. Thus, in this state, a step signal as shown in FIG. 2(b) is applied to deflection coil 6Y and, if a constant signal is applied to deflection coil 6X, the electron beam is deflected stepwise across the surface of the specimen. For example, in the first step, the electron beam irradiates point p in FIG. 3, and the electrons having undergone an energy loss thereat are analyzed in the energy analyzer l4 and detected by detector 16. The detected signal is then added to the step signal in the adding circuit 19 and the added output of said circuit 19 is applied to coil IOY of the cathode-ray tube 11. The energy analyzer is swept by the sweep signal generator 17 through a fixed energy range, the signal generated by said generator 17 also being applied to coil 10X of the cathode-ray tube 11. As a result, an energy distribution waveform C. as shown in FIG. 4 is displayed on the screen of the cathode-ray tube 11. Then, in the second step, the electron beam irradiates point p in FIG. 3. The same process is repeated as in the case of point p and an energy distribution waveform C is displayed on said screen and so on until all the distribution waveforms from points p, p represented by C C, are displayed on the screen as shown in FIG. 4. In FIG. 4, the abscissa X indicates the energy, and the ordinate Y indicates the electron beam intensity and the distance from the grain boundary.

In the embodiment constituted as described above, the shift of the plasma loss in the vicinity of the grain boundary of compound metals can be measured within a very short period of time, moreover, said shift can be displayed as a function of the distance from the grain boundary. Furthermore, since the ratio of the size of the signal supplied to deflection coil 6Y by the step signal generator 9 and the size of the signal applied to coil 10Y of the cathode-ray tube 11 (Le, the magnification) can be precisely ascertained in advance, the distance from the grain boundary can be accurately ascertained by measuring the distance between the scanning image magnification and the base line of C,, C C As clearly shown in FIG. 4, not only the shift of the plasma loss, but the intensity variation of the distribution waveforms can be compared and ascertained, thereby making plasma loss measurement extremely useful.

It goes without saying that this invention is not lim ited to the above-described embodiment. Application possibilities are extremely wide. For example, this invention can be applied to a spectroscopic analyzing de vice in which an electron beam or X-ray beam etc. irradiates a specimen from which characteristic X-rays are secondarily generated in the same way as in the above described embodiment. In this case, however, the energy analyzer would need to be replaced by a goniometer equipped with a spectroscopic crystal or a non dispersive solid detector (S.S.D). Again, this invention can be applied to an E.S.C.A. (electron spectroscopy for chemical analysis) or an Auger electron analyzer.

Having thus described my invention with the detail and the particularity as required by the Patent Laws, what is desired protected by Letters Patent is set forth in the following claims:

I. In a device for scanning a high energy beam over a specimen in a raster in the X and Y directions by X and Y axis beam deflection devices and detecting a signal indicative of the interaction between the beam and the specimen and producing an image on a C.R.T. by brightness modulation of the intensity of the CRT. beam with said detected signal, said C.R.T. having X and Y axis C.R.T. deflection devices synchronized with said X and Y axis beam deflection devices; the im' provement comprising an energy analyzer positioned relative to the specimen to detect the distribution of energies of the beam after interaction with the specimens as the analyzer is swept by a sawtooth signal which varies the energy level detected and means associated therewith comprising a step signal generator for stepwise application of deflection signals to the beam deflection device and a sawtooth generator in synchronism with the step signal generator for simultaneously sweeping the X-axis C.R T. deflection device and the energy analyzer, means for adding the output of the energy analyzer and the step signal generator and applying to the Y-axis C.R.T. deflection device such that en ergy distribution curves for spaced points on a specimen are displayed on the CRT. separated by Y-axis shifts.

2. A display apparatus for displaying the energy dis tribution of charged particles, said display apparatus incorporating a means for irradiating a specimen with a primary charged particle beam, a deflecting means for varying the irradiating point on the specimen, an analyzer for analyzing the energy of the secondary charged particles emitted from the specimen or the energy loss of the primary charged particles transmitted through the specimen, and a display means in which the display point in the XY plane is determined by the X- axis control means and the Y-axis control means con trolled by the output signal of said analyzer, characterized in that a step signal generator output signal controls said deflecting means digitally, said step signal being applied to Y-axis control means of said display means, and the output signal of sweep signal generator synchronized with said step signal generator controls said analyzer and X-axis control means of said display means. 

1. In a device for scanning a high energy beam over a specimen in a raster in the X and Y directions by X and Y axis beam deflection devices and detecting a signal indicative of the interaction between the beam and the specimen and producing an image on a C.R.T. by brightness modulation of the intensity of the C.R.T. beam with said detected signal, said C.R.T. having X and Y axis C.R.T. deflection devices synchronized with said X and Y axis beam deflection devices; the improvement comprising an energy analyzer positioned relative to the specimen to detect the distribution of energies of the beam after interaction with the specimens as the analyzer is swept by a sawtooth signal which varies the energy level detected and means associated therewith comprising a step signal generator for stepwise application of deflection signals to the beam deflection device and a sawtooth generator in synchronism with the step signal generator for simultaneously sweeping the X-axis C.R.T. deflection device and the energy analyzer, means for adding the output of the energy analyzer and the step signal generator and applying to the Y-axis C.R.T. deflection device such that energy distribution curves for spaced points on a specimen are displayed on the C.R.T. separated by Y-axis shifts.
 2. A display apparatus for displaying the energy distribution of charged particles, said display apparatus incorporating a means for irradiating a specimen with a primary charged particle beam, a deflecting means for varying the irradiating point on the specimen, an analyzer for analyzing the energy of the secondary charged particles emitted from the specimen or the energy loss of the primary charged particles transmitted through the specimen, and a display means in which the display point in the XY plane is determined by the X-axis control means and the Y-axis control means controlled by the output signal of said analyzer, characterized in that a step signal generator output signal controls said deflecting means digitally, said step signal being applied to Y-axis control means of said display means, and the output signal of sweep signal generator synchronized with said step signal generator controls said analyzer and X-axis control means of said display means. 